Flow rate sensor, temperature sensor and flow rate detecting apparatus

ABSTRACT

A flow rate sensor for performing a flow rate detection of fluid with high accuracy without suffering adverse effect of the environmental temperature condition even when the fluid is viscous fluid having relatively high viscosity or the flow rate is relatively small is provided. The flow rate sensor includes a flow rate detector having a heating function and a temperature sensing function, and a pipe line for fluid to be detected which is formed so that heat from the flow rate detector is transferred to and absorbed by the fluid. The temperature sensing which is affected by a heat absorption effect of the fluid due to the heat is executed in the flow rate detector, and the flow rate of the fluid in the pipe line is detected on the basis of the temperature sensing result. Unit retaining portions formed on a casing in which the pipe line is formed, the unit retaining portions being disposed adjacent to the pipe line. A flow rate detecting unit comprising the flow rate detector is retained by the unit retaining portion, and a temperature detecting unit comprising a fluid temperature detector is retained by the unit retaining portion.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention belongs to a fluid flow rate detection technology,and particularly relates to a flow rate sensor and flow rate detectingapparatus for detecting the flow rate of fluid flowing in a pipe line,and to a temperature sensor for detecting temperature of fluid whendetecting the flow rate thereof. The flow rate sensor of the presentinvention is suitably used to accurately measure the flow rate of fluidunder various temperature conditions and to make it easy to fabricatethe flow rate sensor.

Further, the present invention particularly intends to improve themeasurement accuracy of the flow rate sensor, flow rate detectingapparatus and temperature sensor.

(2) Description of Related Art

Various types of sensors have been hitherto used as a flow rate sensor(or flow velocity sensor) for measuring the flow rate (or flow velocity)of various fluid, particularly liquid, and a so-called thermal(particularly indirectly heated type) flow rate sensor is used becausethe cost can be easily reduced.

A sensor in which a thin-film heating element and a thin-filmtemperature sensing element are laminated through an insulating layer ona substrate and the substrate is secured to a pipe line is used as anindirectly heated type flow rate sensor, so that the substrate and thefluid in the pipe line are thermally contacted to each other. By passingcurrent through the heating element, the temperature sensing element isheated to vary the electrical characteristic of the temperature sensingelement such as the value of the electrical resistance of thetemperature sensing element. The electrical resistance value (varied onthe basis of the temperature increase of the temperature sensingelement) is varied in accordance with the flow rate (flow velocity) offluid flowing in the pipe line. This is because a part of the heatingvalue of the heating element is transferred through the substrate intothe fluid, the heating value diffusing into the fluid is varied inaccordance with the flow rate (flow velocity) of the fluid, and theheating value to be supplied to the temperature sensing element isvaried in accordance with the variation of the heating value diffusinginto the fluid, so that the electrical resistance value of thetemperature sensing element is varied. The variation of the electricalresistance value of the temperature sensing element is also varied inaccordance with the temperature of the fluid. Therefore, a temperaturesensing device for temperature compensation is installed in anelectrical circuit for measuring the variation of the electricalresistance value of the temperature sensing element to suppress thevariation of the flow-rate measurement value due to the temperature ofthe fluid at maximum.

An indirectly heated type flow rate sensor using thin film elements asdescribed above is disclosed in JP-08-146026(A), for example.

The conventional indirectly heated type flow rate sensor has a metallicpipe line to be connected external pipe lines. The fluid flows in thepipe line, which is exposed to the outside. Since the metallic pipe linehas high thermal conductivity, the temperature variation of theenvironmental atmosphere is easily transmitted to the fluid in the pipeline, especially to the fluid at the vicinity of inner wall of the pipeline, resulting in lowering the accuracy of detection of the flow rateby the thermal flow rate sensor, especially in case of small amount offlow rate. Such a problem is significant when the difference between thetemperature of the fluid flowing through the pipe line and theenvironmental temperature is great.

The conventional indirectly heated type flow rate sensor is attached tothe external pipe line so that the substrate of a flow rate detector ora casing which is thermally connected to the substrate is exposed fromthe wall surface of the pipe line to the fluid.

For example, the indirectly heated type flow rate sensor disclosed inthe above JP-08-146026(A) as the sensor of high thermal response, highmeasuring accuracy, small size and producibilty with low cost has thefollowing construction:

As shown in FIGS. 31A and 31B, a flow rate sensor 501 is composed of athin film heating element 503, thin film temperature sensing element 504laminated via an insulating layer 505 on a substrate 502, and attachedto an appropriate portion of a pipe line 506 as shown in FIG. 32 inapplication.

In the flow rate sensor 501, the temperature sensing element504 isheated by supplying electric power to the heating element 503, and thechange of the electric resistance value in the temperature sensingelement is detected. The flow rate sensor 501 is disposed on the pipeline 506, and therefore a part of the heating value of the heatingelement 503 is transferred through the substrate 502 into the fluidflowing through the pipe line. The heating value transferred to thetemperature sensing element 504 amounts to the heating value generatedby the heating element subtracted with the heating value diffusing intothe fluid, which is varied in accordance with the flow rate of thefluid. Therefore, the flow rate of the fluid flowing through the pipeline 506 can be detected by detecting the electrical resistance value ofthe temperature sensing element which is varied in accordance with theheating value to be supplied to the temperature sensing element 504.

The dispersing heating value is also varied in accordance with thetemperature of the fluid, and therefore as shown in FIG. 32, atemperature sensor 507 is arranged on an appropriate portion of the pipeline 506, and electrical resistance value of the temperature sensingelement is also varied in accordance with the temperature of the fluid.Therefore, a temperature sensing device for temperature compensation isinstalled in an electrical circuit for measuring the variation of theelectrical resistance value of the temperature sensing element tosuppress the variation of the flow-rate measurement value due to thetemperature of the fluid at maximum.

However, since the conventional flow rate sensor 501 is directlyconnected to the metallic pipe line 506 which is exposed to the outside,the heating value posessed by the fluid is dissipated to the outside orthe heating value is supplied to the fluid through the metallic pipeline 506 having high thermal conductivity, resulting in that thedetection accuracy of the flow rate sensor 501 is lowered. The influenceof such heat dissipation on the detection accuracy of the flow ratesensor is significant when the flow rate of the fluid is very small, andmore significant when the specific heat of the fluid is small.

When the fluid is viscous fluid, particularly viscous fluid havingrelatively high viscosity, particularly liquid, the flow-velocitydistribution on the section perpendicular to the flow of the fluid inthe pipe line 506 is more remarkable so as to show a parabolic curvehaving an extreme value at the central portion, that is, theflow-velocity at the central part greatly didders from the flow velocityat the vicinity of the wall of pipe line. In the case of theconventional sensor in which the substrate 502 or the casing 508connected to the substrate is merely exposed to the fluid at the wall ofthe pipe line, the flow-velocity distribution has a great effect on theprecision of the flow-rate measurement. This is because the flowvelocity of the fluid flowing at the center portion on the section ofthe pipe line is not taken into consideration, but only the flowvelocity of the fluid in the neighborhood of the wall of the pipe lineis taken into consideration. As described above, the conventional flowrate sensor has such a problem that it is difficult to measure the flowrate of fluid accurately when the fluid is viscous fluid havingrelatively high viscosity.

Even when fluid has low viscosity at room temperature, it induces aproblem connected to the above viscosity problem because the viscosityof the fluid increases as the temperature is lowered.

Further, the above problem is more remarkable when the flow rate perunit time is relatively low than when the flow rate per unit time ishigh.

In order to improve the detection accuracy of the indirectly heated typeflow rate sensor, it is important to transmit the heat value generatedby the heater to the temperature sensor under the influence of only theheat absorption by the fluid. In the conventional indirectly heated typeflow rate sensor, however, the heat transmission between the environmentand the temperature sensor or heater cannot be ignored as mentioned inthe above, and the detected flow rate value is varied in accordance withthe environmental temperature, resulting in occurrence of the error inthe flow rate detection.

The flow rate sensor is required to be used under an extremely broadtemperature environment in accordance with a geographical condition, anindoor or outdoor condition, etc. Further, these conditions are addedwith a season condition, a day or night condition, etc., and thetemperature environment is greatly varied, especially in the outdoorcondition. Therefore, there has been required a flow rate sensor whichcan detect the flow rate accurately under such a broad environmentaltemperature condition as described above.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a flow ratesensor or flowmeter which can accurately measure the flow rate of fluidon by preventing the influence of the environmental temperaturecondition on the measuring accuracy.

Further, an object of the present invention is to make it easy tofabricate the thermal flow rate sensor or flowmeter.

Further, an object of the present invention is to provide a flow ratesensor or flowmeter which can accurately measure the flow rate of fluidflowing in a pipe line even when the fluid is viscous fluid havingrelatively high viscosity.

Further, an object of the present invention is to provide a flow ratesensor or flowmeter which can accurately measure the flow rate of fluidflowing in a pipe line even when the flow rate is relatively small.

Still further, an object of the present invention is to provide a flowrate sensor or flowmeter which can accurately measure the flow rate offluid even when the specific heat is small or the flow rate is small byreducing the heating value dissipated from the flow rate sensor to thecasing or the outside.

Further, an object of the present invention is to provide a flow ratesensor or flowmeter which can be attached easily to the casing to bestably fixed thereto and has sufficient durability.

Further, an object of the present invention is to provide a temperaturesensor for use in measuring the flow rate of the fluid, which has theconstruction similar to the flow rate sensor and can accurately measurethe flow rate of fluid by reducing the heat transmission between theenvironmental atmosphere and the temperature sensor.

In order to attain the above object, according to the present invention,there is provided a flow rate sensor comprising:

a flow rate detector having a heating function and a temperature sensingfunction;

a pipe line for fluid to be detected which is formed so that heat fromthe flow rate detector is transferred to and absorbed by the fluid,wherein the temperature sensing which is affected by a heat absorptioneffect of the fluid due to the heat is executed in the flow ratedetector, and the flow rate of the fluid in the pipe line is detected onthe basis of the temperature sensing result;

at least one unit retaining portion formed on a casing in which the pipeline is formed, the unit retaining portion being disposed adjacent tothe pipe line; and

a flow rate detecting unit comprising said flow rate detector andretained by the unit retaining portion.

In an aspect of the present invention, the casing is made of syntheticresin.

In an aspect of the present invention, the flow rate detecting unitcomprises said flow rate detector, a first heat transfer member providedto the flow rate detector, a first electrode terminal electricallyconnected to the flow rate detector and a first base portion made ofsynthetic resin, the first base portion is retained by the unitretaining portion, the first heat transfer member extends from the firstbase portion into the pipe line, and the first electrode terminalextends from the first base portion to the opposite side to the pipeline.

In an aspect of the present invention, the first heat transfer memberextends to at least the vicinity of the central portion on the sectionof the pipe line.

In an aspect of the present invention, the first base portion comprisesan inner portion having elasticity and an outer portion disposed aroundthe inner portion.

In an aspect of the present invention, a cavity is formed in a centralportion of the first base portion.

In an aspect of the present invention, the first heat transfer memberhas a plate form, and the flow rate detector is joined to a portion ofthe first heat transfer member located in the first base portion.

In an aspect of the present invention, a seal member for the pipe lineis interposed between the first base member and the casing.

In an aspect of the present invention, a device accommodating portion isformed in the casing at the outside of the unit retaining portion, awiring board is disposed in the device accommodating portion.

In an aspect of the present invention, the device accommodating portionis covered by a lid portion.

In an aspect of the present invention, the flow rate detector comprisesa thin-film heating element and a flow rate detecting thin-filmtemperature sensing element disposed so as to be affected by the effectof the heating of the thin-film heating element, the thin-film heatingelement and the flow rate detecting thin-film temperature sensingelement being formed on a first substrate.

In an aspect of the present invention, the first heat transfer member isjoined to the first substrate.

In an aspect of the present invention, the thin-film heating element andthe flow rate detection thin-film temperature sensing element arelaminated on a first surface of the first substrate through a firstinsulating layer.

In an aspect of the present invention, the first heat transfer member isjoined to a second surface of the first substrate.

In an aspect of the present invention, the dimension of the first heattransfer member in the direction of the pipe line is set to be largerthan the dimension in the direction perpendicular to the extensiondirection of the first heat transfer member within the section of thepipe line.

In an aspect of the present invention, the flow rate sensor furthercomprises a temperature detecting unit retained by the unit retainingportion other than that for retaining the flow rate detecting unit, thetemperature detecting unit including a temperature detector fordetecting the temperature of the fluid in the pipe line for compensationwhen the flow rate of the fluid in the pipe line is detected.

In an aspect of the present invention, the temperature detecting unitcomprises said temperature detector, a second heat transfer memberprovided to the temperature detector, a second electrode terminalelectrically connected to the temperature detector and a second baseportion made of synthetic resin, the second base portion is retained bythe unit retaining portion other than that for retaining the flow ratedetecting unit, the second heat transfer member extends from the secondbase portion into the pipe line, and the second electrode terminalextends from the second base portion to the opposite side to the pipeline.

In an aspect of the present invention, the second heat transfer memberextends to at least the vicinity of the central portion on the sectionof the pipe line.

In an aspect of the present invention, the second base portion comprisesan inner portion having elasticity and an outer portion disposed aroundthe inner portion.

In an aspect of the present invention, a cavity is formed in a centralportion of the second base portion.

In an aspect of the present invention, the second heat transfer memberhas a plate form, and the temperature detector is joined to a portion ofthe second heat transfer member located in the second base portion.

In an aspect of the present invention, a seal member for the pipe lineis interposed between the second base member and the casing.

In an aspect of the present invention, the wiring board and the secondelectrode terminal of the temperature detecting unit are electricallyconnected to each other.

In an aspect of the present invention, the temperature detectorcomprises a temperature detection thin-film temperature sensing elementon the second substrate.

In an aspect of the present invention, the second heat transfer memberis joined to the second substrate.

In an aspect of the present invention, the temterature detectionthin-film temperature sensing element are laminated on a first surfaceof the second substrate through a second insulating layer.

In an aspect of the present invention, the second heat transfer memberis joined to a second surface of the second substrate.

In an aspect of the present invention, the dimension of the second heattransfer member in the direction of the pipe line is set to be largerthan the dimension in the direction perpendicular to the extensiondirection of the second heat transfer member within the section of thepipe line.

In order to attain the above object, according to the present invention,there is also provided a flow rate sensor comprising:

a flow rate detector having a heating function and a temperature sensingfunction;

a pipe line for fluid to be detected which is formed so that heat fromsaid flow rate detector is transferred to and absorbed by the fluid,wherein the temperature sensing which is affected by a heat absorptioneffect of the fluid due to the heat is executed in said flow ratedetector, and the flow rate of the fluid in said pipe line is detectedon the basis of the temperature sensing result; and

a casing made of synthetic resin.

In order to attain the above object, according to the present invention,there is also provided a flow rate detecting unit or flow rate sensorfor use in a flow rate sensor including a flow rate detector having aheating function and a temperature sensing function in which thetemperature sensing which is affected by a heat absorption effect offluid due to the heat is executed and the flow rate of the fluid isdetected on the basis of the temperature sensing result, the flow ratedetecting unit comprising:

the flow rate detector;

a first heat transfer member provided to the flow rate detector;

a first electrode terminal electrically connected to the flow ratedetector; and

a first base portion made of synthetic resin, wherein the first heattransfer member and the first electrode terminal extends to the oppositeside to each other.

In order to attain the above object, according to the present invention,there is also provided a fluid temperature detecting unit or fluidtemperature sensor for use in a flow rate sensor including a flow ratedetector having a heating function and a temperature sensing function inwhich the temperature sensing which is affected by a heat absorptioneffect of fluid due to the heat is executed and the flow rate of thefluid is detected on the basis of the temperature sensing result inorder to perform compensation of the flow rate detected due to thetemperature of the fluid, the temperature detecting unit comprising:

a temperature detector;

a second heat transfer member provided to the temperature detector;

a second electrode terminal electrically connected to the temperaturedetector; and

a second base portion made of synthetic resin, wherein the second hea ttransfer member and the second electrode terminal extends to theopposite si de to each other.

In order to attain the above object, according to the present invention,there is also provided a flow rate sensor comprising:

a flow rate detector having a heating function and a temperature sensingfunction;

a pipe line for fluid to be detected; and

a flow rate detection heat transfer member which is disposed so as to beaffected by heat from the flow rate detector and extends into the pipeline,

wherein the temperature sensing which is affected by a heat absorptioneffect of the fluid due to the heat via the flow rate detection heattransfer member is executed in the flow rate detector, and the flow rateof the fluid in the pipe line is detected on the basis of thetemperature sensing result, and, the flow rate detector and a portion ofthe flow rate detection heat transfer member thermally connected to theflow rate detector are sealed within a flow rate detection base portionmade of synthetic resin having a thermal conductivity of 0.7 [W/m.K] orless.

In an aspect of the present invention, the flow rate detection baseportion is made of synthetic resin having a thermal conductivity of 0.4[W/m.K] or less.

In an aspect of the present invention, the flow rate detection baseportion extends in a radial direction of the pipe line and passesthrough a central axis of the pipe pine.

In an aspect of the present invention, the flow rate detection heattransfer member has a plate form being disposed in the pipe line alongthe pipe line.

In an aspect of the present invention, the flow rate detector comprisesa thin-film heating element and a flow rate detecting thin-filmtemperature sensing element disposed so as to be affected by the effectof the heating of the thin-film heating element outside the pipe line,the thin-film heating element and the flow rate detecting thin-filmtemperature sensing element being formed on a first substrate.

In an aspect of the present invention, the flow rate sensor furthercomprises a fluid temperature detector to perform compensation of theflow rate detected in the flow rate detection, wherein the fluidtemperature detector and a fluid temperature detection heat transfermember disposed so as to extend into the pipe line are thermallyconnected to each other.

In an aspect of the present invention, the flow rate detector and aportion of the temperature detection heat transfer member thermallyconnected to the flow rate detector are sealed within a temperaturedetection base portion made of synthetic resin having a thermalconductivity of 0.7 [W/m.K] or less.

In an aspect of the present invention, the temperature detection baseportion is made of synthetic resin having a thermal conductivity of 0.4[W/m.K] or less.

In an aspect of the present invention, the temperature detection baseportion extends in a radial direction of the pipe line and passesthrough a central axis of the pipe pine.

In an aspect of the present invention, the temperature detection heattransfer member has a plate form being disposed in the pipe line alongthe pipe line.

In an aspect of the present invention, the flow rate sensor furthercomprising heating control means for controlling the heating of theheating element connected to a passage for supplying electric current tothe heating element, wherein the heating control means controls thecurrent to be supplied to the heating element on the basis of thetemperature sensing result so that the temperature sensing result iscoincident with a target value, and the flow rate of the fluid isdetected on the basis of the control state of the heating control means.

In order to attain the above object, according to the present invention,there is also provided a flow rate sensor comprising;

a flow rate detector having a heating element and a temperature sensingelement formed on a substrate;

a fin plate for transferring heat to fluid to be detected therethrough,and

an output terminal for outputting the voltage value corresponding to theflow rate, wherein the flow rate detector, a part of the fin plate and apart of the output terminal are coated by molding.

In an aspect of the present invention, the flow rate detector is fixedto an end surface of the fin plate, the flow rate detector and theoutput terminal are connected to each other via a bonding wire.

In an aspect of the present invention, the fin plate and the outputterminal are manufactured by processing a plate to a plate base memberand then processing the plate base member to the fin plate and theoutput terminal.

In an aspect of the present invention, the plate base member is formedby etching the plate.

According to the present invention, there is provided a flow ratedetecting apparatus comprising:

the flow rate sensor as described in the above;

a casing having a sensor hole for accommodating the flow rate sensor;and

a fluid flow passage pipe having an opening disposed at a positioncorresponding to the sensor hole.

In an aspect of the present invention, a seal member is interposedbetween the flow rate sensor and the sensor hole.

In an aspect of the present invention, the flow rate detecting apparatusfurther comprising a fluid temperature sensor, wherein a sensor hole foraccommodating the temperature sensor is formed in the casing and anopening disposed at a position corresponding to the sensor hole foraccommodating the temperature sensor in the fluid flow passage pipe.

In an aspect of the present invention, a seal member is interposedbetween the temperature sensor and the sensor hole for accommodating thetemperature sensor.

According to the present invention, there is provided a flow rate sensorcomprising;

a flow rate detector having a heating element and a temperature sensingelement formed on a substrate; and

a recess portion formed in the substrate, the recess portion beingsealed with an air layer formed therein.

In an aspect of the present invention, the recess portion is formed byetching.

In an aspect of the present invention, the recess portion is sealed by aglass plate.

In an aspect of the present invention, the flow rate sensor furthercomprises a fin plate performing heat transmission to the fluid, whereinthe flow rate detector is fixed to a surface of an end portion of thefin plate so that a side of the flow rate detector on which the heatingelement and the temperature sensing element is positioned confront thesurface of the end portion of the fin plate.

According to the present invention, there is provided a flow rate sensorcomprising:

a flow rate detector having a heating element and a temperature sensingelement with an insulator interposed therebetween;

a fin plate an end portion of which is joined to the flow rate detector;

an output terminal electrically connected to the flow rate detector; and

a housing made of resin accommodating the flow rate detector,

wherein the fin plate and the output terminal extend to the outside ofthe housing, a cavity is provided in the housing and the flow ratedetector is disposed in the cavity.

In an aspect of the present invention, the end portion of the fin platejoined to the flow rate detector and an end portion of the outputterminal connected to the flow rate detector are positioned in thecavity.

In an aspect of the present invention, the end portion of the fin platejoined to the flow rate detector and an end portion of the outputterminal connected to the flow rate detector are positioned in thecavity.

In an aspect of the present invention, the end portion of the fin platejoined to the flow rate detector and an end portion of the outputterminal connected to the flow rate detector are positioned in thecavity.

In an aspect of the present invention, a notched portion is formed on anouter peripheral surface of the housing.

In an aspect of the present invention, the housing comprises a main bodyportion having a recess portion and a lid portion covering the recessportion.

According to the present invention, there is also provided a temperaturesensor comprising;

a temperature detector having a temperature sensing element and aninsulator laminated on the temperature sensing element;

a fin plate an end portion of which is joined to the temperaturedetector;

an output terminal electrically connected to the temperature detector;and

a housing made of resin accommodating the temperature detector,

wherein the fin plate and the output terminal extend to the outside ofthe housing, a cavity is provided in the housing and the temperaturedetector is disposed in the cavity.

In an aspect of the present invention, the end portion of the fin platejoined to the temperature detector and an end portion of the outputterminal connected to the emperature detector are positioned in thecavity.

In an aspect of the present invention, a notched portion is formed on anouter peripheral surface of the housing.

In an aspect of the present invention, the housing comprises a main bodyportion having a recess portion and a lid portion covering the recessportion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cut-out side view showing an embodiment of a flowrate sensor according to the present invention;

FIG. 2 is a cross-sectional view showing the embodiment of the flow ratesensor according to the present invention;

FIG. 3 is an exploded perspective view showing a flow rate detector ofthe embodiment of the flow rate sensor according to the presentinvention;

FIG. 4 is a circuit diagram showing the embodiment of the flow ratesensor according to the present invention;

FIG. 5 is a cross-sectional view showing a modification of a flow ratedetecting unit of the flow rate sensor according to the presentinvention;

FIG. 6 is a cross-sectional view showing a modification in attaching theflow rate detecting unit to a unit retaining portion of the flow ratesensor according to the present invention;

FIG. 7 is a cross-sectional view showing an embodiment of the flow ratesensor according to the present invention, taken along a pipe line forfluid flowing;

FIG. 8 is a cross-sectional view showing the embodiment of the flow ratesensor according to the present invention, taken perpendicularly to apipe line for fluid flowing;

FIG. 9 is a cross-sectional view showing a flow rate sensing unit of theflow rate sensor according to the present invention;

FIG. 10 is a circuit diagram showing the embodiment of the flow ratesensor according to the present invention;

FIG. 11 is a graph showing a relationship between a flow rate and anoutput voltage in the embodiment of the flow rate sensor according tothe present invention;

FIG. 12 is a graph showing a relationship between a flow rate and anoutput voltage in a comparative flow rate sensor;

FIG. 13 is a graph showing a variation of the output voltage with timelapse in the flow rate sensor according to the present invention;

FIGS. 14A and 14B are front sectional view and side sectional viewshowing a flow rate sensor according to the present invention;

FIG. 15 is an exploded, perspective view showing the flow rate detectorof the flow rate sensor according to the present invention;

FIG. 16 is a longitudinal sectional view showing the flow rate detectorof the flow rate sensor;

FIG. 17 is an explanatory diagram showing a manufacturing process of theflow rate sensor;

FIG. 18 is a cross-sectional view showing a flow rate sensormanufactured by the process of FIG. 17;

FIG. 19 is a cross-sectional view showing a flow rate detectingapparatus including the flow rate sensor;

FIG. 20 is a cross-sectional view showing the flow rate detectingapparatus including the flow rate sensor;

FIG. 21 is a cross-sectional view showing a flow rate sensor comprisinga fin plate and a flow rate detector mounted thereon and the flow ratedetecting apparatus including the flow rate sensor;

FIG. 22 is an exploded perspective view showing an embodiment of a flowrate sensor according to the present invention;

FIG. 23 is a cross-sectional view showing the flow rate sensor of FIG.22 where a lid portion is separated from a body portion;

FIG. 24 is an exploded perspective view showing a flow rate detector;

FIG. 25A is an exploded perspective view showing another embodiment ofthe flow rate sensor according to the present invention;

FIG. 25B is a cross-sectional view showing the flow rate sensor of FIG.25A;

FIG. 26A is an exploded perspective view showing still anotherembodiment of the flow rate sensor according to the present invention;

FIG. 26B is a cross-sectional view showing the flow rate sensor of FIG.26A;

FIG. 27 is an exploded perspective view showing a temperature detectorused in the flow rate sensor according to the present invention;

FIG. 28 is a cross-sectional view showing the flow rate detectingapparatus according to the present invention;

FIG. 29 is a cross-sectional view showing the flow rate detectingapparatus;

FIG. 30 is a graph showing a variation of an output variation rate withtime lapse in the flow rate sensor according to the present inventionand the comparative flow rate sensor;

FIG. 31A is a perspective view showing a flow detector of a conventionalflow rate sensor;

FIG. 31B is a cross-sectional view showing the flow detector of theconventional flow rate sensor; and

FIG. 32 is a cross-sectional view showing the flow detector of theconventional flow rate sensor attached to a pipe line.

PREFERRED EMBODIMENTS FOR EXECUTING THE INVENTION

Embodiments of the present invention will be described with reference tothe drawings.

FIG. 1 is a partially cut-out side view showing an embodiment of a flowrate sensor according to the present invention, and FIG. 2 is across-sectional view of FIG. 1.

In these figures, 2 represents the main body portion of a casing, and apipe line 4 serving as a flow passage for fluid to be detected is formedso as to penetrate through the casing main body portion. The pipe line 4extends to both the ends of the casing main body portion 2. Connectionportions 6 a, 6 b (e.g. external thread) for connecting to an externalpipe are formed at both ends of the casing main body portion. The casingmain body portion 2 is made of a synthetic resin, for example vinylchloride resin, or glass fiber reinforced polyphenylen sulfide (PPS) orpolybutylene terephthalate (PBT) having good chemical-resistance andoil-resistance, etc. A device accommodating portion is formed at theupper side of the pipe line 4 in the casing 2, and a casing lid portion8 is fixed to the accommodation portion by a screw or tight fitting. Thecasing is constructed by the casing lid portion 8 and the casing mainbody portion 2.

In this embodiment, two device unit retaining portions 50, 60 are formedat the bottom (i.e. side near the pipe line 4) of the deviceaccommodating portion 5 of the casing main body portion 2 so as to beadjacent to the pipe line 4. The unit retaining portions 50, 60 each hasa cylindrical inner surface having a symmetrical axis extending inradial direction of the pipe line 4. A flow rate detecting unit 51 isretained by the first retaining portion 50, and a temperature detectingunit 61 is retained by the second retaining portion 60.

The flow rate detecting unit 51 has a flow rate detector 12, a fin plate14 serving as a heat transfer member joined to the flow rate detector 12via an adhesive member 16 having good thermal conduction property,electrode terminals 52, bonding wires 28 electrically connectingelectrodes of the flow rate detector 12 to the corresponding electrodeterminals 52, a base portion 53 made of synthetic resin. The baseportion 53 comprises two portions which are different from each other,one of which is an inner portion 53-1 and the other is an outer portion53-2. The inner portion 53-1 is elastic and is made of fluororubber forexample, so that it can be deformed by absorbing stress caused due tothe difference in thermal expansion property among the casing main bodyportion 2 and members of the flow rate detecting unit 51 on the basis ofthe temperature variation. The outer portion 53-2 is hard,chemical-resistant and oil-resistant, and is made of polyphenylensulfide (PPS) or polybutylene terephthalate having goodchemical-resistance and oil-resistance, etc. The base portion 53 has acylindrical outer surface corresponding to the inner surface of theretaining portion 50. A part of the fin plate 14 extends from the baseportion 53 into the pipe line 4, while a part of the electrode terminal52 extends from the base portion 53 toward the opposite side (outside).That is, the flow rate detector 12, the adhesive member 16, a part ofthe fin plate 14 and a part of the electrode terminal 52 are sealed withthe base portion 53.

As shown in FIG. 3, the flow rate detector 12 is designed in a chipstructure by forming an insulating layer 12-2 on the upper surface(first surface) of a substrate 12-1, forming a thin-film heating element12-3 on the insulating layer 12-2, forming on the heating element a pairof electrode layers 12-4, 12-5 for the thin-film heating element,forming an insulating layer 12-6 thereon, forming a flow rate detectionthin-film temperature sensing element 12-7 on the insulating layer 12-6and then forming an insulating layer 12-8 on the flow rate detectionthin-film temperature sensing element 12-7. As the substrate 12-1 may beused a member which is set to about 0.5 mm in thickness and about 2 to 3mm in square and also formed of silicon or alumina (when an insulatingsubstrate of alumina or the like is used, the insulating layer 12-2 maybe omitted), and as the thin-film heating element 12-3 may be used amember of cermet which is set to about 1 μm in thickness and designed ina desired shape by patterning. As the electrode layers 12-4, 12-5 may beused a member which is formed of nickel at a thickness of about 0.5 μmor a member obtained by laminating gold layer on the above member at athickness of about 0.1 μm. The insulating layers 12-2, 12-6, 12-8 may beformed of SiO₂ at a thickness of about 1 μm. As the thin-filmtemperature sensing element 12-7 may be used a metal resistant filmhaving a large and stable temperature coefficient such as platinum ornickel which is patterned into a desired shape, for example, ameandering shape at a thickness of about 0.5 to 1 μm (or may be used amember formed of NTC thermistor of manganese oxide). The thin-filmheating element 12-3 and the thin-film temperature sensing element 12-7are disposed so as to be extremely proximate to each other through thethin-film insulating layer 12-6 as described above, whereby thethin-film temperature sensing element 12-7 is immediately affected bythe effect of the heating of the thin-film heating element 12-3.

As shown in FIG. 2, a fin plate 14 serving as a heat transfer member isjoined to one surface of the flow rate detector 12, that is, the secondsurface of the substrate 12-1 by a joint member 16 having excellentthermal conductivity. The fin plate 14 may be formed of copper,duralumin, copper-tungsten alloy or the like. Silver paste may be usedas the joint member 16. An opening through which the fin plate 14 ispenetrated is formed at the position in the casing main body portion 2at which the flow rate detector 12 is disposed.

As shown in FIGS. 1 and 2, an O-ring 54 as a sealing member for the pipe4 is disposed between the outer peripheral surface of the base portion53 and the inner surface of the unit retaining portion 50.

The upper portion of the fin plate 14 is connected to the flow ratedetector 12 while the lower portion thereof extends into the pipe line4. The fin plate 14 extends into the pipe line 4 having a substantiallycircular shape so as to pass through the center on the section of thepipe line 4 and traverse from the upper portion to the lower portion ofthe pipe line 4. However, the pipe line 4 is not necessarily circular insection, but may have a proper sectional shape. In the pipe line 4, thedimension L₁ of the fin plate 14 in the pipe direction is sufficientlylarger than the thickness L₂ of the fin plate 14. Therefore, the finplate 14 can excellently transfer heat between the flow rate detector 12and the fluid without greatly affecting the flow of the fluid in thepipe line 4.

In the casing main body portion 2, the unit retaining portion 60 isdisposed at a position which is separated from the unit retainingportion 50 along the pipe line 4. The temperature detector 61 isretained by the unit retaining portion 60.

The temperature detecting unit 61 has a temperature detector 22, a finplate 14′ serving as a heat transfer member joined to the temperaturedetector 22 via an adhesive member having good thermal conductionproperty, electrode terminals 62, bonding wires 29 electricallyconnecting electrodes of the temperature detector 22 to thecorresponding electrode terminals 62, a base portion 63 made ofsynthetic resin. The base portion 63 comprises two portions which aredifferent from each other, one of which is an inner portion 63-1 and theother is an outer portion 63-2. The inner portion 63-1 is elastic and ismade of fluororubber for example, so that it can be deformed byabsorbing stress caused due to the difference in thermal expansionproperty among the casing main body portion 2 and members of thetemperature detecting unit 61 on the basis of the temperature variation.The outer portion 63-2 is hard, chemical-resistant and oil-resistant,and is made of polyphenylen sulfide (PPS) or polybutylene terephthalatehaving good chemical-resistance and oil-resistance, etc. The baseportion 63 has a cylindrical outer surface corresponding to the innersurface of the retaining portion 60. A part of the fin plate 14′ extendsfrom the base portion 63 into the pipe line 4, while a part of theelectrode terminal 62 extends from the base portion 63 toward theopposite side (outside). That is, the temperature detector 22, a part ofthe fin plate 14′ and a part of the electrode terminal 62 are sealedwith the base portion 63.

The temperature detector 22 is designed in such a chip structure that athin-film temperature sensing element for the temperature compensationof the fluid similar to that of the flow rate detector 12 is formed on asubstrate similar to that of the flow rate detector 12. That is, thetemperature detector 22 has the same construction as shown in FIG. 3with the exception that the thin-film heating element 12-3, a pair ofelectrode layers 12-4, 12-5 and the insulating layer 12-6 are omitted.The temperature detector 22 is connected to the fin plate 14′ via ajoining member as in the case of the flow rate detector 12.

The temperature detecting unit 61 is preferably positioned at theupstream side of the flow rate detecting unit 51 relative to the flowingdirection of the fluid in the pipe 4.

In the accommodating portion 5 of the casing body portion 2, a wiringboard 26 is fixedly disposed. Some electrodes of the wiring board 26 areelectrically connected to the electrodes 52 of the flow rate detectingunit 51 by wire bonding etc. (not shown), and also to the electrodes 62of the temperature detecting unit 61 by wire bonding etc. (not shown).Some other electrodes of the wiring board 26 are connected to externallead wires 30, and the external lead wires 30 extend to the outside ofthe casing.

FIG. 4 is a diagram showing the circuit construction of the flow ratesensor of this embodiment. As shown in FIG. 5, the voltage of a DC powersource 40 is applied to the thin-film heating element 12-3 and thebridge circuit 42. An output indicating the flow rate is obtained from adifferential amplifier 44 in the bridge circuit 42. That is, in the flowrate detector 12, the thin-film temperature sensing element 12-7executes the temperature sensing operation which suffers the heatabsorption effect of the fluid to be detected through the fin plate 14due to the heating of the thin-film heating element 12-3, and the flowrate of the fluid to be detected in the pipe line 4 is detected on thebasis of the temperature sensing result and the result of compensationdue to the fluid temperature detected by the temperature detector 22through the fin plate 14′.

FIG. 5 is a cross-sectional view showing a modification of the flow ratedetecting unit 51 of the above embodiment. In the flow rate detectingunit 51, a cavity 55 is formed at the central portion of the baseportion 53, i.e. the central portion of the inner portion 53-1. The flowrate detector 12 is disposed in the cavity 55. The thermal influence ofthe environment on the flow rate detector 12 can be reduded on the basisof the adiabatic effect of the cavity 55. A vent hole 56 is provided onthe base portion for communicating the cavity 55 to the deviceaccommodating portion 5. The temperature detecting unit 61 may also havethe cavity and the vent hole.

FIG. 6 is a cross-sectional view showing a modification of theinstalltation of the flow rate detecting unit 51 into the unit retainingportion 50 of the above embodiment. In FIGS. 1 and 2, an O-ring retainedgroove is formed on both the inner surface of the unit retaining portion50 and the outer surface of the flow rate detecting unit 51, whereas inthe modification of FIG. 6 the O-ring retained groove 57 is formed onlyon the inner surface of the unit retaining portion 50. The O-ringretained groove may be formed only on the outer surface of the flow ratedetecting unit 51. The installation of the temperature detecting unit 61into the unit retaining portion 60 may be performed in the same manneras the flow rate detecting unit 51.

According to the above embodiment, the casing main body portion 2 isformed of the synthetic resin having low thermal conductivity, andtherefore the variation of the environmental temperature does notimmediately influence the temperature of the fluid in the pipe 4 and theflow rate detection can be performed with less influence of theenvironmental temperature variation.

According to the above embodiment, the flow rate detecting unit 51having the flow rate detector 12 is retained by the unit retainingportion 50 and the temperature detecting unit 61 having the temperaturedetector 22 is retained by the unit retaining portion 60, and thereforethe fabrication work in the manufacturing process can be easilyperformed.

Since the fin plates 14, 14′ are used, an accurate flow rate detectioncan be performed with sufficiently reflecting the flow rate distributioneven when the fluid to be detected is viscous fluid having relativelyhigh viscosity, and further for any type of flow rate distribution inthe radial direction on the section of the pipe line 4. Accordingly,even when the flow rate is relatively minute or under a broadenvironmental temperature condition, the flow rate of the fluid flowingin the pipe can be accurately measured.

In the above embodiment, the fin plates 14, 14′ are disposed so as topass through the center portion on the section of the pipe line andtraverse from the upper portion to the lower portion of the pipe line.However, the fin plates 14, 14′ may be disposed so as to extend from theupper portion on the section of the pipe line to the vicinity of thecentral portion. With this construction, for any type flow ratedistribution in the radial direction on the section of the pipe line 4,the flow rate detection can be accurately performed with excellentlyreflecting the flow rate distribution.

FIGS. 7 and 8 are cross-sectional views showing an embodiment of theflow rate sensor according to the present invention. FIG. 7 shows across section taken along the fluid flow passage pipe and FIG. 7 shows across section taken perpendicularly to the fluid flow passage pipe. Inthese figures, members having the same functionns as those in FIGS. 1and 2 are indicated by the same reference numerals. “A” denotes acentral axis of the pipe 4.

In this embodiment, connection portions 6 a, 6 b (e.g. quick couplingmechanism; not shown in detail) for connecting the sensor to theexternal pipe line are formed at both ends of the casing main bodyportion 2. The unit retaining portions 50, 60 each has a steppedcylindrical inner surface having a symmetrical axis extending in radialdirection of the pipe 4. The flow rate detecting unit 51 having astepped cylindrical outer surface is retained by the first retainingportion 50, and the temperature detecting unit 61 having a steppedcylindrical outer surface is retained by the second retaining portion60.

FIG. 9 is a cross-sectional views showing the flow rate detecting unit51. As shown in FIG. 9, the flow rate detecting unit 51 has a flow ratedetector 12, a fin plate 14 serving as a heat transfer member joined tothe flow rate detector 12 via an adhesive member 16 having good thermalconduction property, electrode terminals 52, bonding wires 28electrically connecting electrodes of the flow rate detector 12 to thecorresponding electrode terminals 52, and a base portion 53 made ofsynthetic resin. The base portion 53 is preferably made of syntheticresin having low thermal conductivity (i.e. heat insulation property)and good chemical-resistance and oil-resistance. The base portion 53 hasa stepped cylindrical outer surface corresponding to the inner surfaceof the retaining portion 50. A part of the fin plate 14 extends from thebase portion 53 into the pipe line 4, while a part of the electrodeterminal 52 extends from the base portion 53 toward the opposite side(outside). That is, the flow rate detector 12, the adhesive member 16, apart of the fin plate 14, a part of the electrode terminal 52 and thebonding wire 28 are sealed with the base portion 53.

The temperature detecting unit 61 differs from the flow rate detectingunit 51 essentially in using the temperature detector instead of theflow rate detector 12. That is, the temperature detecting unit 61 has afin plate 14′ serving as a heat transfer member joined to thetemperature detector 22 via an adhesive member having good thermalconduction property, electrode terminals 62, bonding wires electricallyconnecting electrodes of the temperature detector 22 to thecorresponding electrode terminals 62, and a base portion made ofsynthetic resin. A part of the fin plate 14′ extends from the baseportion into the pipe line 4, while a part of the electrode terminal 62extends from the base portion toward the opposite side (outside).

The temperature detector is designed in such a chip structure that athin-film temperature sensing element for the fluid temperaturecompensation similar to that of the flow rate detector 12 is formed on asubstrate similar to that of the flow rate detector 12. That is, thetemperature detector has the same construction as shown in FIG. 3 withthe exception that the thin-film heating element 12-3, a pair ofelectrode layers 12-4, 12-5 and the insulating layer 12-6 are omitted.The temperature detector is connected to the fin plate 14 via a joiningmember as in the case of the flow rate detector 12.

As shown in FIG. 7, an O-ring 64 serving as a seal member for the pipe 4is disposed between the outer surface of the flow rate detecting unit 61and the inner surface of the unit retaining portion 60.

In the accommodating portion 5 of the casing body portion 2, a pressingplate 32 for the flow rate detecting unit 51 and the temperaturedetecting unit 61, and a wiring board 26 is fixedly disposed thereon.Some electrodes of the wiring board 26 are electrically connected to theelectrodes 52 of the flow rate detecting unit 51 by wire bonding etc.(not shown), and also to the electrodes 62 of the temperature detectingunit 61 by wire bonding etc. (not shown). Some other electrodes of thewiring board 26 are connected to external lead wires 30, and theexternal lead wires 30 extend to the outside of the casing. The externallead wires 30 may be integrally formed on a predetermined position ofthe casing main body portion 2 in advance, so that the external leadwires 30 are electrically connected to the wiring board 26 when thewiring board 26 is attached to the main body portion 2.

FIG. 10 is a diagram showing the circuit construction of a flow ratesensor according to the present invention. A supply power source is setto +15V(±10%), for example, and it is supplied to a constant-voltagecircuit 102. The constant-voltage circuit 102 has an output of 0.1W at+6V (±3%), and the output thereof is supplied to the bridge circuit 104.The bridge circuit 104 contains a flow rate detection temperaturesensing element 104-1 (the above 12-7), a temperature compensationtemperature sensing element 104-2 and variable resistors 104-3, 104-4.

The voltages at points a and b are applied to a differential amplifyingcircuit 106. The amplification factor of the differential amplifyingcircuit 106 is made variable by a variable resistor 106 a. The output ofthe differential amplifying circuit 106 is input to an integratingcircuit 108. The differential amplifying circuit 106 whose amplificationfactor is variable and the integrating circuit 108 function asresponsibility setting means as described later.

The supply power source is connected to the collector of an NPNtransistor 110, and the emitter of the transistor 110 is connected to aheating element 112 (the above 12-3). The output of the integratingcircuit 108 is input to the base of the transistor 110. That is, thesupply power source supplies current through the transistor 110 to theheating element 112 (that is, applies a voltage to the heating element112, makes current flow through the heating element and supplies power),and the voltage to be applied to the heating element 112 is controlledby a divided voltage of the transistor 110. The divided voltage of thetransistor 110 is controlled by the output current of the integratingcircuit 108 input to the base through the resistor, and the transistor110 functions as a variable resistor and as heating control means forcontrolling the heating of the heating element 112.

In the flow rate detector 12, the temperature sensing of the thin-filmtemperature sensing element 12-7 is carried out in the flow ratedetector 12 with being affected by the heat absorption of the fluid tobe detected through the fin plate 14 due to the heating of the thin-filmheating element 12-3. As a result of the temperature sensing, thedifference between the voltages Va, Vb at the points a, b of the bridgecircuit 104 shown in FIG. 10 is obtained.

The temperature of the flow rate detection temperature sensing element104-1 is varied in accordance with the flow rate of the fluid, resultingin variation of the value of (Va-Vb). By setting the resistance valuesof the variable resistors 104-3, 104-4 to proper values in advance, thevalue of (Va-Vb) can be set to zero when the flow rate of the fluid isequal to a desired value serving as a reference. At this reference flowrate, the output of the differential amplifying circuit 106 is equal tozero, and the output of the integrating circuit 108 is fixed, so thatthe resistance value of the transistor 110 is also fixed. In this case,the divided voltage to be applied to the heating element is also fixed,and the flow rate output at this time indicates the above reference flowrate.

If the flow rate of the fluid is increased or reduced from the referenceflow rate, the output of the differential amplifying circuit 106 isvaried in polarity (which differs in accordance with thepositive/negative sign of the resistance-temperature characteristic ofthe flow rate detection temperature sensing element 104-1) and magnitudein accordance with the value of (Va-Vb), resulting in variation of theoutput of the integrating circuit 108. The variation speed of the outputof the integrating circuit 108 can be adjusted by setting theamplification factor of the differential amplifying circuit 106 with thevariable resistor 106 a. The response characteristic of the controlsystem can be set by the integrating circuit 108 and the differentialamplifying circuit 106.

When the flow rate of the fluid increases, the temperature of the flowrate detection temperature sensing element 104-1 is reduced, and thusthe integrating circuit 108 supplies the base of the transistor 110 withsuch a control input as to reduce the resistance of the transistor 110so that the heating value of the heating element 112 is increased (thatis, the current to be supplied to the heating element 112 is increased).

On the other hand, when the flow rate of the fluid is reduced, thetemperature of the flow rate detection temperature sensing element 104-1is increased. Therefore, the integrating circuit 108 supplies the baseof the transistor 110 with such a control input as to increase theresistance of the transistor 110 so that the heating value of theheating element 112 is reduced (that is, the current to be supplied tothe heating element 112 is reduced).

As described above, the heat of the heating element 112 is controlled tobe fed back so that the temperature detected by the flow rate detectiontemperature sensing element 104-1 is equal to a target valueirrespective of the variation of the flow rate of the fluid at all times(if occasion demands, the polarity of the output of the differentialamplifying circuit 106 is properly inverted in accordance with thepositive/negative sign of the resistance-temperature characteristic ofthe flow rate detection temperature sensing element 104-1). At thistime, the voltage to be applied to the heating element 112 is matchedwith the flow rate of the fluid and thus it is picked up as the outputof the flow rate.

According to the above embodiment, the temperature of the flow ratedetection temperature sensing element 104-1 around the heating element112 can be kept to a substantially fixed value irrespective of the flowrate of the fluid to be detected, so that the flow rate sensor is notdegraded with time lapse and also occurrence of ignition and explosionof the inflammable fluid to be detected can be prevented.

Further, in this embodiment, no constant-voltage circuit is required tothe heating element 112, and thus there is an advantage that it issufficient to use a low-output constant-voltage circuit 102 for thebridge circuit 104. Therefore, the heating value of the constant-voltagecircuit can be reduced, and the flow rate detection precision can bekept excellent even if the flow rate sensor is miniaturized.

In this embodiment, the base portion 53 of the flow rate detecting unitand the base portion of the temperature detecting unit are each made ofsynthetic resin having a thermal conductivity λ of 0.7 [W/m.K] or lesssuch as epoxy resin containing 40% by weight of amorphous silica(λ=0.60). In such a case, the flow rate detection or the fluidtemperature detection can be performed with little influence of theenvironmental temperature.

The base portion 53 of the flow rate detecting unit and the base portionof the temperature detecting unit are each preferably made of syntheticresin having a thermal conductivity λ of 0.4[W/m.K] or less such asepoxy resin containing 20% by weight of amorphous silica (λ=0.33). Insuch a case, the flow rate detection or the fluid temperature detectioncan be performed with less influence of the environmental temperature,and additionally the flow rate detection can be performed with quickresponse when the flow rate is varied.

FIG. 11 is a graph showing a relationship between the flow rate and theoutput voltage in the flow rate sensor at the fluid temperature of 25°C. Kerosene was used as the fluid to be detected. The inner diameter ofthe fluid flowing passage pipe was set to 4 mmφ. Epoxy resin containing40% by weight of amorphous silica (λ=0.60) was used as material of boththe base portion 53 of the flow rate detecting unit and the base portionof the temperature detecting unit. The detection was performed under theenvironmental temperatures of 15° C. and 35° C. FIG. 12 is a graphshowing the same relationship as FIG. 11 with the exception that it wasobtained under the condition where the epoxy resin containing 60% byweight of amorphous silica (λ=0.88) was used as material of both thebase portion 53 of the flow rate detecting unit and the base portion ofthe temperature detecting unit. As apparent from the comparison of FIG.11 to FIG. 12, the flow rate detection can be performed with smallervariation of the output voltage due to the variation of theenvironmental temperature in the case of FIG. 11 as compared with thecase of FIG. 12.

FIG. 13 is a graph showing a variation of the output voltage with timelapse in the flow rate sensor when the actual flow rate was varied from20 cc/min to 80 cc/min and thereafter. Kerosene was used as the fluid tobe detected. The inner diameter of the fluid flowing passage pipe wasset to 4 mmφ. The detection was performed The detection was performed intwo cases (X, Y) where epoxy resin containing 20% by weight of amorphoussilica (λ=0.33) for the case X and epoxy resin containing 40% by weightof amorphous silica (λ=0.60) for the case Y were used as material ofboth the base portion 53 of the flow rate detecting unit and the baseportion of the temperature detecting unit. It is apparent that the flowrate detection can be performed with higher responsibility and smallerdetection error in the case of X as compared with the case of Y.

According to the above embodiment, the flow rate detecting base portionfor sealing the flow rate detector is made of synthetic resin having lowthermal conductivity, so that the adverse effect of the thermal transferbetween the outside and the flow rate detector on the flow ratedetection can be suppressed. Therefore, the flow rate of the fluid inthe pipe can be accurately and stably detected under wide environmentaltemperature range.

A preferred embodiment of the flow rate sensor and flow rate detectingapparatus is described hereunder with reference to FIGS. 14A, 14B, 15 to20.

As shown in FIGS. 14A, 14B, the flow rate sensor 201 comprises a flowrate detector 202, a fin plate 203, an output terminal 204 and a coatingmember 205. As shown in FIG. 15, the flow rate detector 206 is designedin such a chip structure that an insulating layer 207, a thin-filmheating element 208, electrode layers 209, 210, an insulating layer 211,a thin-film temperature sensing element 212 and an insulating layer 213are laminated in this order on a substrate 206.

The substrate 206 is formed of a rectangular plate of silicon, aluminaor the like which has a thickness of 600 μm and a size of about 2×3 mm.As shown in FIG. 16, a recess portion 214 having a depth of 550 μm isformed by etching or the like from the opposite surface of the substrateto the surface on which the heating element 208 and the temperaturesensing element 212 are laminated. The depth of the recess portion 214is not specifically restricted, however, it is preferably set so as tobe close to the thickness of the substrate 206 as long as the strengththereof can be maintained. The inner diameter of the recess portion 214is also not specifically restricted, however, it is preferably set so asto be greater than the size of the heating element 208 and thetemperature sensing element 212. A glass plate 215 having a thickness of50 to 200 μm is fixed to the opposite surface of the substrate 206 tothe surface on which the heating element 208 and the temperature sensingelement 212 are laminated to completely seal the recess portion 214.

The heating element 208 is formed of cermet which has a thickness ofabout 1 μm and is designed in a desired shape by patterning, and theelectrode layers 209, 210 are formed of nickel at a thickness of about0.5 μm or formed of a lamination film obtained by laminating a gold filmof about 0.5 μm on a nickel film of about 0.5 μm. The temperaturesensing element 212 has a thickness of about 0.5 to 1 μm and is formedof a metal resistant film of platinum, nickel or the like which ispatterned in a desired shape, for example, a meandering shape and has alarge and stable resistance-temperature coefficient, or an NTCthermistor of manganese oxide. The insulating layers 207, 211, 213 areformed of SiO₂ at a thickness of about 1 μm.

The fin plate 203 is formed of material having excellent thermalconductivity such as copper, duralumin, copper-tungsten alloy or thelike, and it is a rectangular thin plate of 200 μm in thickness andabout 2 mm in width.

As shown in FIG. 14B, the flow rate detector 202 is fixed to the surfaceof the upper end portion of the fin plate 203 through a joint member 216of silver paste or the like so that the surface of the flow ratedetector 202 on which the heating element 208 and the temperaturesensing element 212 are laminated is confronted to the surface of theupper end portion of the fin plate 203. The flow rate detector 202 isconnected to the output terminal 204 by a bonding wire 217, and the flowrate detector 202, the upper half portion of the fin plate 203 and thelower half portion of the output terminal 204 are coated with thecoating member 205 formed by molding.

In the flow rate sensor 201, the recess portion 214 is formed in thesubstrate 206 of the flow rate detector 202 to form an air layer havinga high adiabatic effect in the recess portion 214, and the flow ratedetector 202 is fixed to the surface of the upper end portion of the finplate 203 while the surface of the flow rate detector 202 on which theheating element 208 and the temperature sensing element 212 arelaminated is confronted to the surface of the upper end portion of thefin plate 203, thereby reducing the contact area between the coatingmember 205 and the heating element 208 or the temperature sensingelement 212 at maximum, so that the heating value possessed by thetemperature sensing element 212 or the heating value transferred throughthe fin plate 203 can be suppressed from flowing out of or flowing intothe coating member 205 at maximum.

Accordingly, the sensitivity of the flow rate sensor 201 is not reducedeven when the specific heat of the fluid is small, even when the flowrate is small, etc.

Various methods may be used to manufacture the flow rate sensor 201, andthe fin plate 203 and the output terminal 204 may be unified.

For example, the following process may be adopted. As shown in FIG. 17,there are successively carried out a step of etching a plate 219 to forma plate base member 218 having a predetermined shape (S1), a step ofconducting silver plating treatment on a portion to which the flow ratedetectors 202 will be joined (S2), a step of coating silver paste on theportion to fix the flow rate detector 202 to the portion, connecting theflow rate detector 202 and the output terminal 204 by a bonding wire 217and conducting nickel plating on the portion corresponding to the finplate 203 (S3), and a step of molding the flow rate detector 202, theupper half portion of the fin plate 203 and the lower half portion ofthe output terminal 204 with epoxy resin to form the coating member 221(S4), thereby obtaining the flow rate sensor 201 as shown in FIGS. 18.

As shown in FIGS. 19 and 20, the flow rate detecting device 221comprises a casing 222, a flow passage pipe 223, the flow rate sensor201, a temperature sensor 224, a flow rate detecting circuit board 225,etc.

The casing 222 is formed of synthetic resin such as vinyl chloride resinor the like, and it comprises a main body portion 226 and a lid portion227 detachably attached thereto. Both the end portions of the main bodyportion 226 are designed as connection portions 228 to be connected toan external pipe line, and the fluid passage pipe 223 is disposed so asto penetrate through the main body portion 226.

A sensor insertion space 229 is formed at the upper portion of the mainbody portion 226, and sensor insertion holes 230, 231 are formed so asto extend from the sensor insertion space 229 to the flow passage pipe223.

The flow passage pipe 223 is a circular pipe formed of metal such ascopper, iron, stainless steel or the like, and opening portions 232, 233are formed so as to face the sensor insertion holes 230 and 231.

The temperature sensor 224 comprises a temperature detector (the same asthe temperature detector 22), a fin plate 235, an output terminal 236, acoating member 237, etc., and it has the same construction as the flowrate detector 202 except that it does not have the heating element 208,the electrode layers 209, 210 and the insulating layer 211 of the flowdetector 202. The same method as the flow rate sensor 201 may be adoptedas the method of manufacturing the temperature sensor 224.

The flow rate sensor 201 and the temperature sensor 224 are fitted intothe sensor insertion holes 230 and 231 through the sensor insertionspace 229 of the casing 222. The lower half portions of the fin plates203 and 235 are located in the flow passage pipe 223 so as to penetratethrough the opening portions 232 and 233 of the flow passage pipe 223.The lower ends of the fin plate 203, 235 are set to extend to positionslower than the axial line of the flow passage pipe 223 when the sensorsare fitted. O-rings 238 and 239 are interposed between the flow ratesensor 201 and the sensor insertion hole 230 and between the temperaturesensor 224 and the sensor insertion hole 231 respectively, therebypreventing fluid from leaking through the gaps therebetween.

After the flow rate sensor 201 and the temperature sensor 224 are fittedinto the sensor insertion holes 230 and 231, a sensor press plate 240 isinserted into the sensor insertion space 229 to press the upper surfacesof the coating members 205, 237 of the flow rate sensor 201 and thetemperature sensor 224, and a flow rate detection circuit board 225 ismounted on the sensor press plate 240.

The flow rate detecting circuit board 225 is electrically connected tothe output terminals 204 and 236 of the flow rate sensor 201 and thetemperature sensor 224 (connection is not shown), and the flow ratedetecting circuit described with reference to FIG. 4 is constructed as awhole. That is, in the flow rate sensor 201, the quantity of heatobtained by subtracting the quantity of heat discharged to the fluidthrough the fin plate 203 from the heating value of the heating element208 is detected by a temperature sensing element 212. Further, in thetemperature sensor 224, the heating value owned by the fluid through thefin plate 235 is detected by the temperature sensing element to carryout the fluid temperature compensation, whereby the flow rate of thefluid can be detected with high precision.

In the flow rate sensor 201 of the present invention, the flow ratedetector 202, the upper half portion of the fin plate 203 and the lowerhalf portion of the output terminal 204 are coated with a coating member205 based on molding. Therefore, the flow rate sensor can be surelyinserted into the sensor insertion holes 230, 231, and there can besuppressed such a risk that the heat transferred through the fin plate203 leaks to the casing 222 through the metal flow passage pipe 223 orthe heat is transferred from the casing 222 to the fin plate 203 due toan incomplete sealing state.

From this viewpoint, the sensitivity of the flow rate sensor 201 can beprevented from being lowered even when the specific heat of the fluid issmall, the flow rate is small or the like.

Further, in the flow rate sensor 201 of the present invention, the flowrate detector 202, the upper half portion of the fin plate 203 and thelower half portion of the output terminal 204 are coated and unifiedinto one body by the coating member 205 based on molding, and thetemperature sensor 224 is similar to the case of the flow rate sensor201. Thus, the sensors are merely fitted into the sensor insertion holes230, 231 formed in the casing 222. Therefore, the installation of thesensors 201, 224 into the casing 222 can be extremely easily performed.In addition, it can be kept under a stable fixed state and has highdurability.

FIG. 21 is a cross-sectional view showing a flow rate detectingapparatus for reference, and the flow rate detecting apparatus shown inFIG. 21 has been developed by the inventors of the present invention.

The flow rate detecting apparatus 312 uses a flow rate sensor 301including a flow rate detector 306 which comprises a thin-film heatingelement and a thin-film temperature sensing element laminated on asubstrate 302 through an insulating layer, and an L-shaped fin plate 307having a horizontal plate portion 307 a on which the flow rate detector306 is mounted. In the casing 308, glass 310 is filled in the gapbetween the vertical plate portion 307 b of the fin plate 307 and theopening portion of the flow passage pipe 309 to seal the gap, and theflow rate detector 306 and the overall horizontal plate portion 307 a ofthe fin plate 307 are coated, sealed and fixed by synthetic resin 211,thereby forming the flow rate detecting apparatus 312.

Such problems as discharge of the quantity of heat to the outside orsupply of the quantity of heat from the outside, variation of the flowrate on the cross-section of the pipe and reduction of the measurementprecision of the flow rate due to an outside temperature environmentaleffect or the like can be greatly overcome by using the flow rate sensor301 and the flow rate detecting apparatus 312.

However, the flow rate sensor 301 needs works of joining the flow ratedetector 306 to the horizontal plate portion 307 a of the fin plate 307by a joint member 313, filling the glass 310 in the gap between thevertical plate portion 307 b of the fin plate 307 and the openingportion of the flow passage pipe 309 to seal the gap, coating andsealing the flow rate detector 306 and the overall horizontal plateportion 307 a of the fin plate 307 with the synthetic resin 311.Therefore, the installation work of the flow rate sensor 301 into thecasing 308 is cumbersome and also the fixing state thereof is unstable,so that a problem may occur in durability.

The present invention can also solve the above problem, and provides aflow rate sensor and a flow rate detecting apparatus which can be easilyinstalled into a casing and has sufficiently high durability under astable fixed state.

According to the flow rate sensor of the present invention, the quantityof heat discharged from each part of the flow sensor to the casing andthe outside can be extremely suppressed, and the flow rate can bemeasured with high precision even when the specific heat of fluid issmall, the flow rate of the fluid is small or the like.

Next, preferable embodiments of a flow rate sensor and a temperaturesensor of the present invention will be described with reference toFIGS. 22 to 24, 25A, 25B, 26A, 26B, 27 to 30.

A flow rate sensor 401 shown in FIGS. 22 and 23 comprises a flow ratedetector 402, a fin plate 403, an output terminal 404 and a housing 405.

The flow rate detector 402 is formed by successively forming andlaminating a thin-film temperature sensing resistor 407, an interlayerinsulating layer 8, a thin-film heating element 409, heating elementelectrodes 410, 411 and a protection film 412 on a substrate 406 havinga rectangular plate which is formed of silicon, alumina or the like andhas a thickness of 400 μm and a square of about 2 mm as shown in FIG.24. Reference numeral 413 represents bonding pads to coat the end edgeportions of the temperature sensing resistor 407 to be connected tobonding wires and the heating element electrodes 410, 411 by thin filmof gold (Au) or platinum (Pt).

The temperature sensing resistor 407 comprises a metal resistive film ofplatinum or the like which has a film thickness of about 0.5 to 1 μm anda large and stable temperature coefficient and is patterned in a desiredshape such as a meandering shape, or an NTC thermistor of manganeseoxide.

The interlayer insulating layer 408 and the protection film 412 areformed of SiO₂ at a thickness of about 1 μm .

The heating element 409 comprises a resistor which has a film thicknessof about 1 μm and is patterned in a desired shape, and it is preferablyformed of nickel (Ni), Ni-Cr or Pt, more preferably formed of cermetmaterial such as Ta-SiO₂, Nb-SiO₂ or the like. The heating elementelectrodes 410, 411 are formed of Ni film having a film thickness ofabout 1 μm or a combination of the Ni film and Au film which islaminated on the Ni film and has a film thickness of about 0.5 μm.

The bonding pad 413 is formed of Au of 0.2×0.15 mm in longitudinal andlateral dimensions and about 0.1 μm in thickness.

The fin plate 403 comprises a rectangular thin plate of 200 μm inthickness and about 2 mm in width which is formed of material havingexcellent thermal conductivity such as copper, duralmin, copper-tungstenalloy or the like. The fin plate 403 is designed in an inverse L-shapeso that the upper end portion of the rectangular thin plate issubstantially vertically bent by a proper length. The flow rate detector402 is fixed to the top surface of the bent portion through a jointmember 414 such as silver paste or the like.

The output terminal 404 is a linear thin plate of 200 μm in thicknesswhich is formed of material having high conductivity such as copper orthe like.

The housing 405 comprises a housing main body 415 and a lid 416, andthey are formed of hard resin having high chemical resistance and highoil resistance, and more preferably resin having low thermalconductivity such as epoxy resin, polybutylene terephthalate (PBT),polyphenylene sulfide (PPS) or the like.

The housing main body 415 is designed in such a shallow cylindricalshape that the upper portion thereof is recessed and the inside thereofis set as a hollow recess portion 417, and a fitted portion 415 a whichis obtained by cutting out the housing main body 415 in a recess shapefrom the edge portion of the peripheral wall thereof to the top portionthereof and to which the lid 416 is fitted is formed at the edge portionof the peripheral wall. Further, a projecting step portion 415 b whichis projected in a cylindrical shape is provided to the bottom surface ofthe housing main body 415. The hollow recess portion 417 comprises alarge-diameter recess portion 417 a obtained by circularly holing theinside of the housing main body 415, and a small-diameter recess portion417 b obtained by further circularly holing the center portion of thebottom portion of the large-diameter recess portion.

The lid 416 is designed like a dish which is put face down (the recessportion thereof faces downwardly), and a downwardly-projecting fittingportion 416 a which is fitted to the fitted portion of the housing mainbody is provided at the peripheral edge of the lid 416 so as to bemounted on the top surface of the housing main body 415.

As shown in FIG. 23, in the housing main body 415, the fin plate 403having the flow rate detector 402 fixed to the upper portion thereof isinserted in the small-diameter recess portion 417 b so that the lowerend portion thereof penetrates through the projecting step portion 415 band projects to the outside of the housing while the bent portion of theupper portion thereof is brought into contact with the bottom portion ofthe large-diameter recess portion 417 a and supported by the bottomportion. Four output terminals 404 are provided to the housing main body415 so that one half portion of each output terminal penetrates throughthe side wall of the housing main body and horizontally projects to theoutside of the housing while the other half portion of each outputterminal is joined to and supported by the bottom portion of thelarge-diameter recess portion 417 a. In addition, each output terminal404 and the flow rate detector 402 are bonded to each other by a bondingwire 418.

The lid 416 is put on the housing main body 415 in which the respectiveparts are arranged as described above, and the lid 416 and the housingmain body 415 are fixed to each other by adhesive agent or impregnationto seal the inside of the housing 405, thereby forming the flow ratesensor 401 of this embodiment.

According to the flow rate sensor 401 of this embodiment, the hollowrecess portion 417 of the housing main body 415 is hermetically closedby the lid 416 to form a cavity portion in the housing 405, and the flowrate detector 402 is accommodated in the cavity portion. Accordingly, agas layer (air layer) having high adiabatic effect is formed between thesurrounding of the flow rate detector 402 and the inner peripheralsurface of the housing 405, the surface portion of the fin plate 403 andthe output terminal 404 (containing the connection portions thereof withthe flow rate detector 402) are exposed into the hollow recess portion417, and the contact area between the housing 405 and each of the aboveelements is reduced, so that the quantity of heat transferred from theoutside of the sensor through the housing 405 to the flow rate detector402 can be extremely reduced. In order to prevent dew condensation,dried air, more preferably nitrogen gas, argon gas or the like ispreferably filled in the gas layer.

Accordingly, the effect of the flow-in/out of the quantity of heatbetween the outside air and the flow rate sensor 401 is suppressed, andthe measurement error due to the flow-in of the quantity of heat fromthings other than the fluid is reduced, so that the measurementprecision of the flow rate is enhanced. Therefore, even when thespecific heat of the fluid is small or the flow rate is small, the flowrate can be measured with precision.

The flow rate sensors 401 shown in FIGS. 25A and 25B and FIGS. 26A and26B are different from the above embodiment in the form of the housing405.

The housing 405 shown in FIGS. 25A and 25B comprises a housing main body419 and a lid 420 as in the case of the above embodiment. The housingmain body 419 is provided with a hollow recess portion 421 obtained bycutting out the central portion of the cylinder of the housing main body419 in a recess form from one side portion to the other side portion,and a notched portion 419 d is formed at the outer peripheral surfaceportion of the back surface of the housing main body 419 to have properwidth and depth in order to reduce the thermal contact area between thehousing main body 419 and a casing 452 described later. The lid 420comprises a curved plate which can be joined to the peripheral surfaceof the housing main body, and the lid 420 is mounted on the peripheralsurface of the housing main body 419 to close the hollow recess portion421.

A fitting step portion 419 a for fitting the lid 420 to the housing mainbody 419 is provided at the inside of the peripheral surface of thehousing main body 419, and a projecting step portion 419 which is formedin a cylindrical shape so as to project downwardly is provided at thebottom surface of the housing main body 419.

The housing 405 shown in FIGS. 26A and 26B has the same housing mainbody 419 as the above embodiment, and a lid 422 comprising a bent platewhich is bent in a substantially U-shape. The lid 422 is mounted on thehousing main body 419 to close the hollow recess portion 421. In thiscase, a fitting step portion 419 c for fitting the lid 422 to thehousing main body 419 is provided along the peripheral surface of thelid at the inside of the peripheral surface of the housing main body419. Further, a notched portion 419 d is formed at the outer peripheralsurface portion of the back surface of the housing main body 419 to haveproper width and depth as in the case of the embodiment shown in FIGS.25A and 25B.

In these embodiments, a stripe-shaped fin plate 403 which is not bent inan L-shape is used. The fin plate 403 is inserted through the lowerportion of the hollow recess portion 421 in the housing main body 419,the flow rate detector 402 is fixed to the upper end portion of the finplate 403, and the lower end portion of the fin plate 403 is disposed soas to penetrate through the projecting step portion 419 b and project tothe outside of the housing. The four output terminals 404 are disposedso that the upper end portions thereof penetrate through the upperportion of the hollow recess portion 421 and project to the outside ofthe housing while the lower end portions thereof are disposed in thehollow recess portion 421, and each output terminal 404 and the flowrate detector 402 are connected to each other through a bonding wire418.

The lid 420 or the lid 422 is fitted to the side surface of the housingmain body 419 in which the respective elements are arranged, and theyare fixed to each other by adhesive agent or impregnation to seal theinside of the housing 405, thereby forming the flow rate sensor 401.

In the flow rate sensors 401 of these embodiments, a cavity portion isformed in the housing 405 through the covering of the lid 420 or 422 onthe housing main body 419, and the flow rate detector 402 isaccommodated in the cavity portion. Therefore, the effect of theflow-in/out of the quantity of heat between the outside air and the flowrate sensor 401 can be reduced by the adiabatic effect of an air layerformed around the flow rate detector 402, thereby enhancing themeasurement precision of the flow rate.

Further, a notch portion 419 d is provided at the outer peripheralsurface portion of the housing main body 419, so that it is hard totransfer heat from the surrounding of the sensor and thus the adiabaticeffect is enhanced. That is, under the state that the sensor is mountedon the flow rate detecting apparatus, the notch portion 419 d is notbrought into contact with the peripheral surface of the sensor insertionhole 459, and the portion of the notch portion 419 d is set as a void asshown in FIG. 29, so that the flow-in/out of heat from the casing 452 tothe housing main body 419 is suppressed by the air layer and it iscooperated with the adiabatic effect of the cavity portion formed in thehousing 405 to reduce the measurement error.

The notch portion 419 d may be designed in a proper size and propershape and located at a proper position in conformity with the size,shape, etc. of the housing main body 419, and it may be provided to theouter peripheral surface of the housing main body 415 shown in FIGS. 22,23.

A temperature sensor 431 of the present invention as shown in FIG. 28may be constructed by replacing only the flow rate detector 402 out ofthe constituent elements of the flow rate sensor 401 of each embodimentwith a temperature detector 432 shown in FIG. 27.

That is, the temperature detector 432 is formed by directly andsuccessively laminating an insulating layer 434, a thin-film temperaturesensing element 435 and an insulating layer 436 on the top surface of asubstrate 433, and the shapes and materials of the substrate 433, theinsulating layers 434, 436 and the temperature sensing element 435 arethe same as the flow rate detector 402.

As not shown, the temperature detector 432 is fixed to the end portionof the fin plate 403, the fin plate 403 and the output terminal 404 aredisposed in the housing main body 415, 419 having the hollow recessportion 417, 421, and the temperature detector 432 and the outputterminal 404 are connected to each other by a bonding wire 418. Further,the lid 416, 420, 422 is fitted to the housing main body to hermeticallyclose the hollow recess portion 417, 421 and form the cavity portion inthe housing 405, thereby obtaining the temperature sensor 431 having thesurrounding of the temperature detector 432 as an air layer.

As in the case of the flow rate sensor 401, in the temperature sensor431 thus formed, the temperature detector 432 is accommodated in thecavity portion of the housing 405, the air layer having a high adiabaticeffect is formed between the surrounding of the temperature detector 432and the inner peripheral surface of the housing 405, and the surfaceportion of the fin plate 403 and the output terminal (containing theconnection portions thereof with the temperature detector 432) areexposed to the hollow recess portion. Therefore, the effect on theflow-in/out of the quantity of heat is reduced through the housing 405and the measurement error affecting this quantity of heat is reduced, sothat the measurement precision of the temperature of the fluid can beenhanced.

If the notch portion 419 d is provided at the outer peripheral surfaceportion of the housing main body 415,419, the portion of the notchportion 419 d serves as the void portion to suppress the flow of heatinto/out of the housing main body 415, 419, thereby suppressing themeasurement error effected by undesired quantity of temperature.

The flow rate sensor 401 and the temperature sensor 431 of the presentinvention have common constituent elements, and can be manufactured byvarious methods. Specifically, the constituent elements such as the finplate 403, etc. are mounted in the housing main body 415, 419 which isseparately formed from the above elements, and then the lid 416, 420,422 is mounted on the housing main body 415, 419, or the constituentelements to be fitted to the housing main body are integrally installedinto the housing main body when the housing main body is formed, andthen the lid is mounted on the housing main body.

In the flow rate sensor 401 and the temperature sensor 431 of thepresent invention, the cavity portion is provided in the housing 405 andthe flow rate detector 402 or the temperature detector 432 isaccommodated in the cavity portion so that the surface of each detectoris exposed to the air layer in the cavity portion, whereby the heattransfer from the housing 405 can be prevented and the flow of thequantity of heat into/out of the outside can be suppressed.

Accordingly, if there is adopted such a structure that the flow ratedetector 402 or the temperature detector 432 is accommodated in thecavity portion which is provided in the sensor, any form may be appliedto the housing 405. In the above embodiments, the housing main body andthe lid are designed to be separate from each other for the viewpoint ofthe convenience of the manufacturing. However, another separatestructure or an integral structure of these elements with the respectiveconstituent elements may be adopted.

The flow rate sensor 401 and the temperature sensor 431 thus constructedare fitted into a casing 452 shown in FIGS. 28 and 29 to construct aflow rate detecting apparatus 451, which will be used to measure theflow rate.

The casing 452 is formed of synthetic resin such as vinyl chlorideresin, PBT, PPS or the like, and it comprises a main body portion 455and a lid portion 456 which is detachably mounted on the main bodyportion 455. Both the end portions of the main body portion 455 are setas connection portions 457 to be connected to external pipes, and a flowpassage pipe 453 is disposed so as to penetrate through the main bodyportion 455.

A sensor insertion space 458 is formed at the upper portion of the mainbody portion 455, and sensor insertion holes 459 and 460 are formed soas to extend from the sensor insertion space toward the flow passagepipe 453.

The flow passage pipe 453 is a metal cylindrical pipe formed of copper,iron, stainless steel or the like, and opening portions 461, 462 areformed in the flow passage pipe 453 so as to face the sensor insertionholes 459, 460.

The flow rate sensor 401 and the temperature sensor 431 are fitted fromthe sensor insertion space of the casing 452 into the sensor insertionholes 459, 460. The lower half portions of the fin plates 403 areinserted through the opening portions 461, 462 of the flow passage pipe453 and located in the pipe. When these sensors 401 and 431 are fittedin the sensor insertion holes 459 and 460 respectively, the lower endsof the fin plates 403 extend to positions lower than the central axialline of the flow passage pipe 453.

O-rings 463, 464 are interposed between the flow rate sensor 401 and thesensor insertion hole 459 and between the temperature sensor 431 and thesensor insertion hole 460 to prevent fluid from leaking through the gapstherebetween.

After the flow rate sensor 401 and the temperature sensor 431 arefitted, a sensor press plate 465 is inserted into the sensor insertionspace 458 to press the top surface of the housings 405 of the sensors,and a flow rate, etc. detecting circuit board 454 is mounted thereon.

The flow rate, etc. detecting circuit board 454 is electricallyconnected to the respective output terminals 404 of the flow rate sensor401 and the temperature sensor 431, and the flow rate detecting circuitdescribed with reference to FIG. 10 is constructed as a whole.

Specifically, there is constructed a bridge circuit containing thetemperature sensing resistor 407 of the flow rate detector 402, thetemperature sensing element 435 of the temperature detector 432 and avariable resistor. A constant voltage is applied to the bridge circuitby a constant-voltage circuit, and the output of the bridge circuit isinput through a differential amplifying circuit having an amplificationfactor adjusting resistor and an integration circuit to the baseterminal of a collector-grounded transistor having an emitter terminalwhich is connected to the heating element 409 of the flow rate detector402. The potential of the heating element 409 which varies in accordancewith the potential difference between a,b points of the bridge circuitis picked up as a detection signal for the flow rate.

That is, when the detection temperature of the fluid by the temperaturesensing resistor 407 is lowered, the base current value of thetransistor is controlled on the basis of the signal from the integratedcircuit so as to increase the heating value of the heating element 409,in other words, so as to increase the supply power to the heatingelement. On the other hand, when the detection temperature of the fluidby the temperature sensing resistor 407 is increased, the base currentvalue of the transistor is controlled on the basis of the signal fromthe integrated circuit so as to reduce the heating value of the heatingelement 409, in other words, so as to reduce the supply power to theheating element. Accordingly, irrespective of the flow rate of the fluidto be detected, the temperature compensation of the fluid is carried outso that the flow rate of the fluid can be detected with high precision.

[EXAMPLE]

A flow rate detecting apparatus having the same construction as the flowrate detecting apparatus 451 described above was constructed by usingthe flow rate sensor 401 shown in FIGS. 22 and 23, and the flow rate wasmeasured by using the flow rate detecting apparatus thus constructed.

Kerosene was used as fluid to be measured, and a predetermined amount ofkerosene was put into the flow passage pipe 453. The amount of kerosenewas increased or reduced to a predetermined amount at a time, and theflow rate was continuously measured. Thereafter, the variation of theoutput variation rate with time lapse from the switch time of the flowrate was determined.

The variation of the output variation rate with time lapse from a timepoint at which the flow rate was switched from 20 cc/minute to 80cc/minute is indicated by reference character (A) in FIG. 30. Further,the variation of the output variation rate with time lapse from a timepoint at which the flow rate was switched from 80 cc/minute to 20cc/minute is indicated by reference character (B) in FIG. 30.

Here, the output variation rate indicates the ratio of the measured flowrate value to the actual flow rate value of the fluid flowing throughthe flow passage pipe 453 (i.e., measured flow rate value/actual flowrate value). As the output variation rate approaches to 1.0, it meansthat the measurement error is smaller.

[COMPARATIVE EXAMPLE]

A flow rate sensor having a conventional structure in which thesurrounding of the flow rate detector is covered with no gap by thehousing was installed in the apparatus used in the above Example, andthe flow rate was measured in the same procedure as described above todetermine the output variation rate.

The variation of the output variation rate when the flow rate wasswitched from 20 cc/minute to 80 cc/minute is indicated by referencecharacter (C) in FIG. 30, and the variation of the output variation ratewhen the flow rate was switched from 80 cc/minute to 20 cc/minute isindicated by reference character (D) in FIG. 30.

Referring to FIG. 30, with the conventional flow rate sensor, it takes along time until the measured flow rate value approaches to the actualflow rate value and the output is kept stable (in FIG. 30, 30 seconds ormore are needed, and about 2 minutes are needed in the actualmeasurement). However, with the flow rate sensor of the presentinvention, the output is kept stable within 5 seconds, and it can followthe variation of the actual flow rate in a short time. Therefore, it hasbeen proved that according to the sensor of the present invention, thesensitivity is excellent, the response is high and the measurementprecision is stable and enhanced.

As described above, according to the flow rate sensor and thetemperature sensor of the present invention, the effect of theflow-in/out of the quantity of heat between the outside air and the flowrate sensor or the temperature sensor can be reduced, and even when thespecific heat of the fluid is small, the flow rate is small or the like,the flow rate and the temperature thereof can be measured with highprecision.

[INDUSTRIAL APPLICABILITY]

As described above, according to the flow rate of the present invention,the elements containing the flow rate detector are unified into an unit,and thus the fabrication work in the manufacturing process can be easilyperformed. Further, according to the flow rate sensor of the presentinvention, the measurement of the flow rate can be accurately performedwithout suffering an adverse effect of the variation of the outside airtemperature. Still further, according to the flow rate sensor of thepresent invention, even when the fluid is viscous fluid havingrelatively high viscosity, the flow rate of the fluid flowing in thepipe can be accurately measured. In addition, according to the presentinvention, even when the flow rate is relatively small, the flow rate ofthe fluid flowing in the pipe can be accurately measured.

As described above, according to the flow rate sensor of the presentinvention, the flow rate detecting base portion for sealing the flowrate detector is formed of synthetic resin having low thermalconductivity, so that the adverse effect of the thermal transfer betweenthe outside environment and the flow rate detector on the flow ratedetection can be suppressed. Therefore, the flow rate of fluid to bedetected in a pipe line can be accurately and steadily detected.

The present invention can provide the flow rate sensor and the flow ratedetecting apparatus which can be easily installed into the casing andmounted in the casing under a stable fixed state with sufficientdurability.

Further, according to the flow rate sensor of the present invention, thequantity of heat discharged from each part of the flow rate sensor tothe casing and the outside can be extremely reduced, and even when thespecific heat of the fluid is small, the flow rate is small or the like,the flow rate can be measured with high precision.

As described above, according to the flow rate sensor and thetemperature sensor of the present invention, the effect of theflow-in/out of the quantity of heat between the outside air and the flowrate sensor or the temperature sensor can be suppressed, and thus evenwhen the specific heat of fluid is small, the flow rate is small or thelike, the flow rate and the temperature thereof can be measured withhigh precision.

Reference is made to co-pending U.S. patent application Ser. No.09/763,290 filed Feb. 20, 2001.

What is claimed is:
 1. A flow rate sensor comprising: a flow ratedetector having a heat function and a temperature sensing function; apipe line for fluid to be detected which is formed so that heat from theflow rate detector is transferred to and absorbed by the fluid, whereintemperature sensing which is affected by a heat absorption effect of thefluid due to the heat is executed in the flow rate detector, and theflow rate of the fluid in the pipe line is detected on the basis of thetemperature sensing result; at least one unit retaining portion formedon a casing in which the pipe line is formed, the unit retaining portionbeing disposed adjacent to the pipe line; and a flow rate detecting unitretained by the unit retaining portion, wherein the flow rate detectingunit comprises the flow rate detector, a first heat transfer memberprovided to the flow rate detector, a first electrode terminalelectrically connected to the flow rate detector and a first baseportion made of synthetic resin, the first base portion is retained bythe unit retaining portion, the flow rate detector is sealed within thefirst base portion, the first heat transfer member extends from thefirst base portion into the pipe line, and the first electrode terminalextends from the first base portion to the side opposite the pipe line.2. The flow rate sensor as claimed in claim 1, wherein the casing ismade of synthetic resin.
 3. The flow rate sensor as claimed in claim 1,wherein the first heat transfer member extends to at least the vicinityof the central portion on the section of the pipe line.
 4. The flow ratesensor as claimed in claim 1, wherein the first base portion comprisesan inner portion having elasticity and an outer portion disposed aroundthe inner portion.
 5. The flow rate sensor as claimed in claim 1,wherein a cavity is formed in a central portion of the first baseportion.
 6. The flow rate sensor as claimed in claim 1, wherein thefirst heat transfer member has a plate form, and the flow rate detectoris joined to a portion of the first heat transfer member located in thefirst base portion.
 7. The flow rate sensor as claimed in claim 1,wherein a seal member for the pipe line is interposed between the firstbase member and the casing.
 8. The flow rate sensor as claimed in claim1, wherein a device accommodating portion is formed in the casing at theoutside of the unit retaining portion, a wiring board is disposed in thedevice accommodating portion.
 9. The flow rate sensor as claimed inclaim 8, wherein the device accommodating portion is covered by a lidportion.
 10. The flow rate sensor as claimed in claim 1, wherein thedimension of the first heat transfer member in the direction of fluidflow in the pipe line is larger than the dimension in the directionperpendicular to the direction in which the first heat transfer memberextends into the section of the pipe line and perpendicular to thedirection of fluid flow in the pipe line.
 11. The flow rate sensor asclaimed in claim 1, wherein the flow rate detector comprises a thin-filmheating element and a flow rate detecting thin-film temperature sensingelement disposed so as to be affected by the effect of the heating ofthe thin-film heating element, the thin-film heating element and theflow rate detecting thin-film temperature sensing element being formedon a first substrate.
 12. The flow rate sensor as claimed in claim 11,wherein the first heat transfer member is joined to the first substrate.13. The flow rate sensor as claimed in claim 11, wherein the thin-filmheating element and the flow rate detection thin-film temperaturesensing element are laminated on a first insulating layer which islaminated on a first surface of the first substrate.
 14. The flow ratesensor as claimed in claim 13, wherein the first heat transfer member isjoined to a second surface of the first substrate.
 15. The flow ratesensor as claimed in claim 1, further comprising a temperature detectingunit retained by the unit retaining portion other than that forretaining the flow rate detecting unit, the temperature detecting unitincluding a temperature detector for detecting the temperature of thefluid in the pipe line for compensation when the flow rate of the fluidin the pipe line is detected.
 16. The flow rate sensor as claimed inclaim 15, wherein the temperature detecting unit comprises saidtemperature detector, a second heat transfer member provided to thetemperature detector, a second electrode terminal electrically connectedto the temperature detector and a second base portion made of syntheticresin, the second base portion is retained by the unit retaining portionother than that for retaining the flow rate detecting unit, the secondheat transfer member extends from the second base portion into the pipeline, and the second electrode terminal extends from the second baseportion to the opposite side to the pipe line.
 17. The flow rate sensoras claimed in claim 16, wherein the second heat transfer member extendsto at least the vicinity of the central portion on the section of thepipe line.
 18. The flow rate sensor as claimed in claim 16, wherein thesecond base portion comprises an inner portion having elasticity and anouter portion disposed around the inner portion.
 19. The flow ratesensor as claimed in claim 16, wherein a cavity is formed in a centralportion of the second base portion.
 20. The flow rate sensor as claimedin claim 16, wherein the second heat transfer member has a plate form,and the temperature detector is joined to a portion of the second heattransfer member located in the second base portion.
 21. The flow ratesensor as claimed in claim 16, wherein a seal member for the pipe lineis interposed between the second base member and the casing.
 22. Theflow rate sensor as claimed in claim 16, wherein the wiring board andthe second electrode terminal of the temperature detecting unit areelectrically connected to each other.
 23. The flow rate sensor asclaimed in claim 16, wherein the temperature detector comprises atemperature detection thin-film temperature sensing element on asubstrate.
 24. The flow rate sensor as claimed in claim 23, wherein thesecond heat transfer member is joined to the substrate.
 25. The flowrate sensor as claimed in claim 23, wherein the temperature detectionthin-film temperature sensing element is laminated on an insulatinglayer which is laminated on a first surface of the substrate.
 26. Theflow rate sensor as claimed in claim 25, wherein the second heattransfer member is joined to a second surface of the second substrate.27. The flow rate sensor as claimed in claim 16, wherein the dimensionof the second heat transfer member in the direction of fluid flow in thepipe line is larger than the dimension in the direction perpendicular tothe direction in which the second heat transfer member extends into thesection of the pipe line and perpendicular to the direction of fluidflow in the pipe line.
 28. A flow rate detecting unit for use in a flowrate sensor including a flow rate detector having a heating function anda temperature sensing function in which temperature sensing which isaffected by a heat absorption effect of fluid due to the heat isexecuted and the flow rate of the fluid is detected on the basis of thetemperature sensing result, the flow rate detecting unit comprising: theflow rate detector; a heat transfer member provided to the flow ratedetector; an electrode terminal electrically connected to the flow ratedetector; and a base portion made of synthetic resin, wherein the flowrate detector is sealed within the base portion, and the heat transfermember and the electrode terminal extend from the base portion to thesides opposite each other.
 29. A fluid temperature detecting unit foruse in a flow rate sensor including a flow rate detector having aheating function and a temperature sensing function in which temperaturesensing which is affected by a heat absorption effect of fluid due tothe heat is executed and the flow rate of the fluid is detected on thebasis of the temperature sensing result in order to perform compensationof the flow rate detected due to the temperature of the fluid, thetemperature detecting unit comprising: a temperature detector; a heattransfer member provided to the temperature detector; an electrodeterminal electrically connected to the temperature detector; and a baseportion made of synthetic resin, wherein the temperature detector issealed within the base portion, and the heat transfer member and theelectrode terminal extend from the base portion to the sides oppositeeach other.
 30. A flow rate sensor comprising: a flow rate detectorhaving a heating function and a temperature sensing function; a pipeline for fluid to be detected; and a flow rate detection heat transfermember which is disposed so as to be affected by heat from the flow ratedetector and extends into the pipe line, wherein the temperature sensingwhich is affected by a heat absorption effect of the fluid due to theheat transferred by the flow rate detection heat transfer member isexecuted in the flow rate detector, and the flow rate of the fluid inthe pipe line is detected on the basis of the temperature sensingresult, and, the flow rate detector and a portion of the flow ratedetection heat transfer member thermally connected to the flow ratedetector are sealed within a flow rate detection base portion made ofsynthetic resin having a thermal conductivity of 0.7 W/m K or less. 31.The flow rate sensor as claimed in claim 30, wherein the flow ratedetection base portion is made of synthetic resin having a thermalconductivity of 0.4 W/m.K or less.
 32. The flow rate sensor as claimedin claim 30, wherein the flow rate detection heat transfer memberextends in a radial direction to the pipe line and passes through acentral axis of the pipe line.
 33. The flow rate sensor as claimed inclaim 30, wherein the flow rate detection heat transfer member has aplate form being disposed in the pipe line along the pipe line.
 34. Theflow rate sensor as claimed in claim 32, wherein the flow rate detectorcomprises a thin-film heating element and a flow rate detectingthin-film temperature sensing element disposed so as to be affected bythe effect of the heating of the thin-film heating element outside thepipe line, the thin-film heating element and the flow rate detectingthin-film temperature sensing element being formed on a first substrate.35. The flow rate sensor as claimed in claim 34, further comprisingheating control means for controlling the heating of the heating elementconnected to a passage for supplying electric current to the heatingelement, wherein the heating control means controls the current to besupplied to the heating element on the basis of the temperature sensingresult so that the temperature sensing result is coincident with atarget value, and the flow rate of the fluid is detected on the basis ofthe control state of the heating control means.
 36. The flow rate sensoras claimed in claim 30, further comprising a fluid temperature detectorto perform compensation of the flow rate detected in the flow ratedetection, wherein the fluid temperature detector and a fluidtemperature detection heat transfer member disposed so as to extend intothe pipe line are thermally connected to each other.
 37. The flow ratesensor as claimed in claim 36, wherein the fluid temperature detectorand a portion of the temperature detection heat transfer memberthermally connected to the flow rate detector are sealed within atemperature detection base portion made of synthetic resin having athermal conductivity of 0.7 W/m.K or less.
 38. The flow rate sensor asclaimed in claim 37, wherein the temperature detection base portion ismade of synthetic resin having a thermal conductivity of 0.4 W/m.K orless.
 39. The flow rate sensor as claimed in claim 36, wherein thetemperature detection heat transfer member extends in a radial directionof the pipe line and passes through a central axis of the pipe line. 40.The flow rate sensor as claimed in claim 36, wherein the temperaturedetection heat transfer member has a plate form being disposed in thepipe line along the pipe line.
 41. A flow rate sensor comprising: a flowrate detector having a heat function and a temperature sensing function;a pipe line for fluid to be detected which is formed so that heat fromthe flow rate detector is transferred to and absorbed by the fluid,wherein the temperature sensing which is affected by a heat absorptioneffect of the fluid due to the heat is executed in the flow ratedetector, and the flow rate of the fluid in the pipe line is detected onthe basis of the temperature sensing result; at least one unit retainingportion formed on a casing in which the pipe line is formed, the unitretaining portion being disposed adjacent to the pipe line; and a flowrate detecting unit comprising the flow rate detector and retained bythe unit retaining portion; wherein the flow rate detecting unitcomprises an inner portion having elasticity and an outer portiondisposed around the inner portion.
 42. A flow rate sensor comprising: aflow rate detector having a heat function and a temperature sensingfunction; a pipe line for fluid to be detected which is formed so thatheat from the flow rate detector is transferred to and absorbed by thefluid, wherein the temperature sensing which is affected by a heatabsorption effect of the fluid due to the heat is executed in the flowrate detector, and the flow rate of the fluid in the pipe line isdetected on the basis of the temperature sensing result; at least oneunit retaining portion formed on a casing in which the pipe line isformed, the unit retaining portion being disposed adjacent to the pipeline; and a flow rate detecting unit comprising the flow rate detectorand retained by the unit retaining portion; wherein a cavity is formedin a central portion of the flow rate detecting unit.
 43. A flow ratesensor comprising: a flow rate detector having a heat function and atemperature sensing function; a pipe line for fluid to be detected whichis formed so that heat from the flow rate detector is transferred to andabsorbed by the fluid, wherein the temperature sensing which is affectedby a heat absorption effect of the fluid due to the heat is executed inthe flow rate detector, and the flow rate of the fluid in the pipe lineis detected on the basis of the temperature sensing result; at least oneunit retaining portion formed on a casing in which the pipe line isformed, the unit retaining portion being disposed adjacent to the pipeline; a flow rate detecting unit comprising the flow rate detector andretained by the unit retaining portion; and a temperature detecting unitretained by the unit retaining portion other than that for retaining theflow rate detecting unit, the temperature detecting unit including atemperature detector for detecting the temperature of the fluid in thepipe line for compensation when the flow rate of the fluid in the pipeline is detected; wherein the temperature detecting unit comprises saidtemperature detector, a second heat transfer member provided to thetemperature detector, a second electrode terminal electrically connectedto the temperature detector and a second base portion made of syntheticresin, the second base portion is retained by the unit retaining portionother than that for retaining the flow rate detecting unit, the secondheat transfer member extends from the second base portion into the pipeline, the second electrode terminal extends from the second base portionto the opposite side to the pipe line, and the second base portioncomprises an inner portion having elasticity and an outer portiondisposed around the inner portion.
 44. A flow rate sensor comprising: aflow rate detector having a heat function and a temperature sensingfunction; a pipe line for fluid to be detected which is formed so thatheat from the flow rate detector is transferred to and absorbed by thefluid, wherein the temperature sensing which is affected by a heatabsorption effect of the fluid due to the heat is executed in the flowrate detector, and the flow rate of the fluid in the pipe line isdetected on the basis of the temperature sensing result; at least oneunit retaining portion formed on a casing in which the pipe line isformed, the unit retaining portion being disposed adjacent to the pipeline; a flow rate detecting unit comprising the flow rate detector andretained by the unit retaining portion; a temperature detecting unitretained by the unit retaining portion other than that for retaining theflow rate detecting unit, the temperature detecting unit including atemperature detector for detecting the temperature of the fluid in thepipe line for compensation when the flow rate of the fluid in the pipeline is detected; wherein the temperature detecting unit comprises saidtemperature detector, a second heat transfer member provided to thetemperature detector, a second electrode terminal electrically connectedto the temperature detector and a second base portion made of syntheticresin, the second base portion is retained by the unit retaining portionother than that for retaining the flow rate detecting unit, the secondheat transfer member extends from the second base portion into the pipeline, the second electrode terminal extends from the second base portionto the opposite side to the pipe line, and a cavity is formed in acentral portion of the second base portion.
 45. A flow rate sensorcomprising: a flow rate detector having a heating element and atemperature sensing element formed on a substrate; a fin plate fortransferring heat to fluid to be detected therethrough; and an outputterminal for outputting the voltage value corresponding to the flowrate, wherein the flow rate detector, a part of the fin plate and a partof the output terminal are coated by molding, and the fin plate and theoutput terminal are manufactured by processing a plate to a plate basemember and then processing the plate base member to the fin plate andthe output terminal.
 46. The flow rate sensor as claimed in claim 45,wherein the plate base member is formed by etching the plate.
 47. A flowrate sensor comprising: a flow rate detector having a heating elementand temperature sensing element formed on a substrate; a fin plate fortransferring heat to fluid to be detected therethrough; and an outputterminal for outputting a voltage value corresponding to the flow rate;wherein the flow rate detector, a part of the fin plate to which theflow rate detector is joined, and a part of the output terminal aresealed by molding; wherein the fin plate and the output terminal aremanufactured by processing a plate to a plate base member and thenprocessing the plate base member to the fin plate and the outputterminal.
 48. The flow rate sensor as claimed in claim 47, wherein theplate base member is formed by etching the plate.
 49. A flow ratedetecting apparatus comprising: a flow rate detector having a heatingelement and temperature sensing element formed on a substrate; a finplate for transferring heat to fluid to be detected therethrough; anoutput terminal for outputting a voltage value corresponding to the flowrate, wherein the flow rate detector, a part of the fin plate to whichthe flow rate detector is joined, and a part of the output terminal aresealed by molding; a casing having a sensor hole for accommodating theflow rate sensor; and a fluid flow passage pipe having an openingdisposed at a position corresponding to the sensor hole.
 50. The flowrate detecting apparatus as claimed in claim 48, wherein a seal memberis interposed between the flow rate sensor and the sensor hole.
 51. Theflow rate detecting apparatus as claimed in claim 49, further comprisinga fluid temperature sensor, wherein a sensor hole for accommodating thetemperature sensor is formed in the casing and an opening disposed at aposition corresponding to the sensor hole for accommodating thetemperature sensor in the fluid flow passage pipe.
 52. The flow ratedetecting apparatus as claimed in claim 51, wherein a seal member isinterposed between the temperature sensor and the sensor hole foraccommodating the temperature sensor.
 53. A flow rate sensor comprising:a flow rate detector having a heating element and temperature sensingelement formed on a substrate; a fin plate for transferring heat tofluid to be detected therethrough; and an output terminal for outputtinga voltage value corresponding to the flow rate, wherein the flow ratedetector, a part of the fin plate to which the flow rate detector isjoined, and a part of the output terminal are sealed by molding; whereina recess portion is formed in the substrate, and an air layer is formedin the recess portion sealed by a glass plate.
 54. The flow rate sensoras claimed in claim 53, wherein the recess portion is formed by etching.55. The flow rate sensor as claimed in claim 53, further comprising afin plate performing heat transmission to the fluid, wherein the flowrate detector is fixed to a surface of an end portion of the fin plateso that a side of the flow rate detector on which the heating elementand the temperature sensing element is positioned confront the surfaceof the end portion of the fin plate.